The Common Expression Language (CEL) is an expression language that’s fast, portable, and safe to execute in performance-critical applications. The CEL crate provides a parser and interpreter for the language that emerged from Google, but never provided an implementation for Rust. Given its traits, CEL is the perfect match for any Rust project that requires some sort of expression evaluation. We'll cover why that is the case and where these needs emerged from, then dive into the state of the Rust port of the interpreter, covering some of the challenges met along the way, like reviving the Rust runtime for antlr4.